U.S. Pat. Nos. 4,315,409 and 4,317,665 disclose and claim improvements to cryogenic freezing systems utilizing air at cryogenic temperatures such as disclosed in U.S. Pat. Nos. 3,733,848 and 3,868,827. In the systems of the foregoing patents, air taken from that surrounding the apparatus to be cool ed, e. g., food freezer, is cooled to temperature below -180.degree. F. so that when introduced into the freezer at this temperature quick freezing of articles in the freezer can take place. Such freezers find use in the food industry for quick freezing foods for preservation and shipping of the foods.
The prior art systems rely upon the recirculation of the atmosphere from the freezing compartment after extracting some of the refrigeration by recompression and expansion to achieve the very low temperatures. Problems with the recycle system center on the fact that the federal government requires thorough cleaning and sanitation of this type of equipment. A recycle system embodied in a heavy piece of equipment such as a system including compressors and the like to take air from ambient temperature to below -180.degree. F. are generally not easily opened up for cleaning. Thus such systems are susceptible to frost buildup and the recycle of bacteria particles and frost particles since the atmosphere is constantly reused.